1. Field of the Invention
The invention relates to a technology of determining the presence or absence of occurrence of a malfunction of a cooling apparatus of an internal combustion engine. More particularly, the invention relates to a technology of highly accurately determining the presence or absence of occurrence of a malfunction of a thermostat in the case where coolant that passes via an interior of an internal combustion engine is circulated by an electric pump.
2. Description of Related Art
An internal combustion engine is provided with a cooling apparatus that cools component parts that are heated by heat that is produced by combustion. Such a cooling apparatus includes a thermostat. Due to the thermostat, during a warm-up during which the coolant temperature is below a threshold value, the coolant is circulated without passing through a radiator, and after the coolant temperature reaches the threshold value and the warm-up is completed, the coolant is circulated via the radiator. In this manner, the internal combustion engine is quickly warmed up, and is kept at an appropriate temperature. However, in the case where the thermostat becomes abnormal due to fixation or the like, the coolant can sometimes circulates via the radiator even during a warm-up, in which case the internal combustion engine cannot be quickly warmed up. Therefore, there is a need to highly accurately determine whether or not the cooling apparatus is abnormal.
To this end, Japanese Patent Application Publication No. 2004-263613 (JP-A-2004-263613) discloses a thermostat malfunction detection apparatus capable of detecting malfunction of a thermostat relatively highly accurately and easily even during a partially warmed-up state. This thermostat malfunction detection apparatus is a thermostat malfunction detection apparatus that detects malfunction of a thermostat provided in a circulation route of a coolant (cooling water) of an engine on the basis of a detected temperature of the cooling water and a temperature of the cooling water estimated on the basis of the state of operation of the engine, and that is characterized in that when the water temperature detected at the time of beginning the estimation of the water temperature satisfies a prescribed temperature condition, an electric fan that sends wind to the circulation route is driven.
According to the thermostat malfunction detection apparatus disclosed in the aforementioned patent application publication, it is determined that the engine is in partially warmed-up state, when the water temperature detected at the time of beginning the estimation of the water temperature satisfies the prescribed temperature condition. Therefore, merely by determining whether the rise of the detected water temperature is gentle, it can be determined whether or not the thermostat has an open-circuit malfunction. Hence, malfunction of the thermostat can easily be detected even during the partially warmed-up state.
However, in the case where coolant in a medium passage in a cooling apparatus is circulated by an electric water pump, there is possibility of false determination of the presence or absence of malfunction of the thermostat.
If an electric pump starts to be operated during operation of the internal combustion engine, the coolant heated due to the operation of the internal combustion engine passes as the electric pump is operated. Therefore, the detection value provided by a sensor that detects the coolant temperature rises temporarily. As a result, there is a possibility of false determination when the presence or absence of malfunction of the thermostat is to be determined through the use of the detection value from the sensor.
The water pump of the thermostat malfunction detection apparatus disclosed in the foregoing patent application publication uses the engine as a motive power source, and the aforementioned problems are not considered at all in conjunction with the disclosed construction.